The present invention generally relates to micro-electro-mechanical system (MEMS) technology suitable for the fabrication of microfluidic systems. More particularly, the present invention relates to a microfluidic valve for controlling fluid flow in a microfluidic system. The microfluidic valve includes a diaphragm controlled to move between a first position to provide a small aperture and a second position to provide a large aperture. The small aperture prevents fluid flow through the valve due to increased capillary and entry resistance forces between the fluid and the valve in the small aperture. The large aperture permits fluid flow through the valve due to reduced capillary forces between the fluid and the valve in the large aperture.
MEMS technology integrates electrical components and mechanical components on a common silicon substrate by using microfabrication technology. Integrated circuit (IC) fabrication processes, such as photolithography processes and other microelectronic processes, form the electrical components. The IC fabrication processes typically use materials such as silicon, glass, and polymers. Micromachining processes, compatible with the IC processes, selectively etch away areas of the IC or add new structural layers to the IC to form the mechanical components. The integration of silicon-based microelectronics with micromachining technology permits complete electro-mechanical systems to be fabricated on a single chip. Such single chip systems integrate the computational ability of microelectronics with the mechanical sensing and control capabilities of micromachining to provide smart devices.
One type of MEMS is a microfluidic system. Microfluidic systems include components such as channels, reservoirs, mixers, pumps, valves, chambers, cavities, reaction chambers, heaters, fluidic interconnects, diffusers, nozzles, and other microfluidic components. These microfluidic components typically have dimensions between a few micrometers and a few hundreds of micrometers. These small dimensions minimize the physical size, the power consumption, the response time and the waste of the microfluidic system. Such microfluidic systems may provide wearable miniature devices located either outside or inside the human body.
Applications for microfluidic systems include genetic, chemical, biochemical, pharmaceutical, biomedical, chromatography, IC cooling, ink-jet printer head, medical, radiological, environmental, as well as any devices that require liquid or gas filled cavities for operation. Such application may involve processes related to analysis, synthesis and purification. The medical applications include diagnostic and patient management such as implanted drug dispensing systems. The environmental applications include detecting hazardous materials or conditions such as air or water pollutants, chemical agents, biological organisms or radiological conditions. The genetic applications include testing and/or analysis of DNA.
Examples of microfluidic systems, constructed using MEMS technology, are disclosed in U.S. Pat. No. 5,962,081 (Ohman, et al.), U.S. Pat. No. 5,971,355 (Biegelsen, et al.), U.S. Pat. No. 6,048,734 (Burns, et al.), U.S. Pat. No. 6,056,269 (Johnson, et al.), U.S. Pat. No. 6,073,482 (Moles), U.S. Pat. No. 6,106,245 (Cabuz), U.S. Pat. No. 6,109,889 (Zengerle, et al.), U.S. Pat. No. 6,227,809 (Forster, et al.), U.S. Pat. No. 6,227,824 (Stehr), U.S. Pat. No. 6,126,140 (Johnson, et al.), U.S. Pat. No. 6,136,212 (Mastrangelo, et al.), U.S. Pat. No. 6,143,248 (Kellogg, et al.), and U.S. Pat. No. 6,265,758 (Takahashi), and in a technical paper entitled xe2x80x9cPreliminary Investigation of Micropumping Based On Electrical Control Of Interfacial Tensions,xe2x80x9d by Hirofumi Matsumoto and James E. Colgate, of the Department of Mechanical Engineering at Northwestern University, Evanston, Ill., IEEE, 1990, pages 105-110, CH2832-4/90/0000-0105. Examples of systems, constructed using electrowetting and surface tension, are disclosed in a technical paper entitled xe2x80x9cDynamics of Electrowetting Displays,xe2x80x9d by G. Beni and M. A. Tenan, of Bell Laboratories, Holmdel, N.J., J. Appl. Phys. 52(10), October 1981, pages 6011-6015, 0021-8979/81/106011-05, and U.S. Pat. No. 4,417,786 (Beni, et al.), respectively.
In a microfluidic system, microfluidic valves control the flow of the fluid through the channels or between the other microfluidic components, such as the reservoirs, mixers, pumps, and chambers. Microfluidic valves have been constructed using actuation methods such as electrostatic, magnetic, piezoelectric, bimorph, thermo pneumatic, and pressure sensitive capillary forces. For example, U.S. Pat. No. 6,143,248 (Kellogg, et al.) discloses a microfluidic valve that uses rotationally induced fluid pressure to overcome capillary forces between the fluid and the microfluidic component. Fluids which completely or partially wet the material of the microfluidic component which contains them experience a resistance to flow when moving from a microfluidic component having a small cross-section to one having a large cross-section, while those fluids which do not wet these materials resist flowing from microfluidic components having a large cross-section to those with a small cross-section. This capillary pressure varies inversely with the sizes of the adjacent microfluidic components, the surface tension of the fluid, and the contact angle of the fluid on the material of the microfluidic component. By varying the intersection shapes, materials and cross-sectional areas of the microfluidic components, the valve is made to induce fluid flow for a particular pressure on the fluid for a particular application. However, the operation of this microfluidic component is dependent upon an external rotational force to change the pressure of the fluid induced on the microfluidic component. In some microfluidic applications, it would be desirable to have a microfluidic valve that actively controls fluid flow in a microfluidic system, having a relatively constant fluid pressure.
Accordingly, there is a need for a microfluidic valve that actively controls fluid flow in a microfluidic system, having a relatively constant fluid pressure, based on a change in the capillary and entry resistance forces between the fluid and the valve.
A valve is adapted to control the flow of the fluid in a microfluidic system. The valve includes an input port adapted to receive a fluid exerting a predetermined level of pressure on the valve and an output port adapted to provide the fluid. The valve further includes a tubular body having a variable sized aperture therein adapted to vary between a first aperture size and a second aperture size, larger than the first aperture size. The first aperture prevents the flow of the fluid through the valve responsive to a first level of capillary forces between the fluid and the valve body at the first aperture. The second aperture permits the flow of the fluid through the valve responsive to a second level of capillary forces, less than the first level of capillary forces, between the fluid and the valve in the second aperture.
These and other aspects of the present invention are further described with reference to the following detailed description and the accompanying figures, wherein the same reference numbers are assigned to the same features or elements illustrated in different figures. Note that the figures may not be drawn to scale. Further, there may be other embodiments of the present invention explicitly or implicitly described in the specification that are not specifically illustrated in the figures and vise versa.